The present invention generally relates to vapor compression systems and, more particularly, to vapor compression refrigeration, freezer and air conditioning systems. In this regard, an important aspect of the present invention concerns improvements in the efficiency of vapor compression refrigeration systems which are advantageously suited for use in commercial medium and low temperature refrigeration/freezer applications.
Vapor compression refrigeration systems typically employ a fluid refrigerant medium that is directed through various phases or states to attain successive heat exchange functions. These systems generally employ a compressor which receives refrigerant in a vapor state (typically in the form of a super heated vapor) and compresses that vapor to a higher pressure which is then supplied to a condenser wherein a cooling medium comes into indirect contact with the incoming high pressure vapor, removing latent heat from the refrigerant and issuing liquid refrigerant at or below its boiling point corresponding to the condensing pressure. This refrigerant liquid is then fed to an expansion device, for example, an expansion valve or capillary tube, which effects a controlled reduction in the pressure and temperature of the refrigerant and also serves to meter the liquid into the evaporator in an amount equal to that required to provide the intended refrigeration effect. As suggested in the prior art, for example, U.S. Pat. No. 4,888,957, a flashing into vapor of a small portion of the liquid refrigerant can occur, however, in such instances, the discharge from the valve is in the form of a low temperature liquid refrigerant with a small vapor fraction. The low temperature liquid refrigerant is vaporized in the evaporator by heat transferred thereto from the ambient environment to be cooled. Refrigerant vapor discharged from the compressor is then returned to the compressor for continuous cycling as described above.
As described in my co-pending U.S. application Ser. No. 09/228,696, the disclosure of which is herein incorporated by reference, for high efficiency operation, it is desired to efficiently utilize as much of the cooling coil in the evaporator as possible. Such high-efficiency operation entails maximum utilization of the latent heat of evaporation along as much of the cooling coil(s) as possible.
Typical prior art systems, particularly those employed in commercial refrigeration/freezer systems, however, commonly utilize a condenser which communicates with the expansion device (e.g. a thermostatic expansion valve) through relatively long refrigeration lines and, in addition, place the expansion device in close proximity to the evaporator. As a result, refrigerant is supplied to the evaporator, in liquid form or substantially in liquid form with only a small vapor fraction. This refrigerant feed and the low flow rates inherently associated therewith produce relatively inefficient cooling particularly along the initial portions of the cooling coil(s) resulting in the build-up of frost or ice at such locations which further reduces the heat transfer efficiency thereof. In commercial systems, such as open refrigerated display cabinets, the build-up of frost can reduce the rate of air flow to such an extent that an air curtain is weakened resulting in an increased load on the case. Moreover, this build-up of frost or ice on the evaporator cooling coils necessitates frequent defrosting, thereby reducing the shelf-life of food products contained in the refrigeration/freezer cabinets and increasing the power consumption and cost of operation.
The present invention overcomes the foregoing problems and disadvantages of conventional vapor compression refrigeration systems by providing a vapor compression refrigeration system in which the inlet to the evaporator is supplied with a refrigerant liquid and vapor mixture wherein the amount of vapor in, and the flow rate of, the mixture at the inlet (and throughout the refrigerant path) cooperate to achieve and maintain improved heat transfer along substantially the entire length of the cooling coil(s) in the evaporator.
It is, therefore, an object of the present invention as to provide a vapor compression refrigeration method and apparatus having improved heat transfer efficiency along substantially the entire length of the cooling coils in the evaporator.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus wherein the build-up of ice or frost on the surfaces of the cooling coils, particularly those cooling coil surfaces closest to the evaporator inlet, is substantially reduced, thereby significantly minimizing the need for the defrosting thereof.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus wherein the build-up of moisture or frost on the surfaces of product contained in refrigeration cases and freezers associated therewith is significantly reduced, if not virtually eliminated.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus characterized by improved temperature consistency along the entire length of the cooling coils thereof.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus characterized by reduced power consumption and cost of operation.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus having improved heat transfer efficiency and reduced refrigerant charge requirements, enabling in many applications the elimination of traditional components such as, for example, a receiver in the refrigeration circuit.
Another object of the present invention is to provide a vapor compression refrigeration method and apparatus wherein the temperature differential between the cooling coils and air circulated in heat exchange relationship therewith is minimized, resulting in substantially reduced extraction of the water content in that air and the maintenance of more uniform humidity levels in refrigeration cases and freezer compartments associated therewith.
Another object of the present invention is to provide a commercial refrigeration system wherein the compressor, expansion device and condenser can be remotely located from the refrigeration or freezer compartment associated therewith, thereby facilitating the servicing of those components without interference with customer traffic and the like.
Another object of the present invention is to provide a vapor compression refrigeration system wherein the compressor, expansion device and condenser, together with their associated controls, are contained as a group in a compact housing which can be easily installed in a refrigeration circuit.